Cystic Fibrosis (CF) is a disorder primarily involving the exocrine glands, and we have begun to study cyclic nucleotides, which may be essential determinants of secretion in CF. Present topics are: (1) the concentration and distribution of cyclic AMP and cyclic GMP in normal and CF body fluids, (2) the response of cyclic AMP to beta receptor stimulation in normal and CF lymphocytes and fibroblasts, (3) the response of cyclic GMP to stimulation of the cholinergic receptor in several systems, (4) levels and response to physiologic stimuli of circulating norepinephrine, epinephrine, and dopamine-hydrolxylase, measures of sympathetic nervous system activity in CF, and (5) measurement of number and binding affinity of beta-receptors in CF tissues.